A dye sensitized solar cell (DSSC) is a photovoltaic system which uses a semiconductor formed of a nanoparticulate or nanoporous metal oxide to provide a high surface area structure, a dye (typically comprising an organic or metal complex component) adsorbed onto the semiconductor to produce excited electrons from absorbed light and an electrolyte in contact with both the dye and the counter electrode. The electrodes of a DSSC include an optical electrode generally in the form of a transparent conducting oxide (TCO) which is supported on a light transmissible substrate and a counter electrode separated from the anode by the electrolyte, semiconductor and dye.
U.S. Pat. No. 4,927,721 and U.S. Pat. No. 5,084,365 disclose one of the first practical DSSCs (referred to as the Grätzel cell). It contained a liquid electrolyte and ruthenium dye-coated sintered titanium dioxide. The energy conversion efficiency (ECE) of this type of DSSC has been reported to be as high as 10.4% although variation in performance and reproducibility mean that typically much lower ECEs of ca 5% are reliably obtained. The manufacture of DSSCs typically requires a high temperature sintering process that has limited the substrate to rigid light transmissible materials such as glass.
The Grätzel DSSC contains electrolyte in the form of a solution containing corrosive iodine in an organic solvent and raises problems of leakage and long term operational stability. The use of gel/polymer electrolytes, molten salts, hole transport materials or plastic crystals have been proposed as potential alternatives. Ionic liquids that contain the iodide/triiodide redox are viscous liquids and thus reduce the potential for leakage problems. Grätzel et al in Adv. Mater. 19, 1133-1137, (2007) have shown that ionic liquids in DSSC have high cell performance and good stability properties. In recent years, there has been an interest to find alternatives to liquid electrolytes, which contain the iodide/triodide redox system, that has seen the development of organic charger carrier materials, referred to as hole transport materials. For example, solid state DSSC devices that contain doped hole transport materials, such as SpiroMeOTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene), have been shown to produce moderate efficiencies by Grätzel et al in Adv. Mater. 17, 813-815 (2005).
Kroon (J. M. Kroon et al, Prog. Photovolt. Res. Appl. 15, 1-18 (2007)) describes the use of blocking layers to improve the performance of DSSC by retarding the electron recombination at the electrode interface. In addition, Law (Law et al, J. Phys. Chem. B. 110, 22652-22663 (2006)) has shown that coating the photoanode by means of high temperature (300° C. for TiCl4) ALD enhanced the efficiency of ZnO nanowire DSSCs.
The present invention can provide a DSSC with improved properties. Said properties include one or more of the following: efficiency, short circuit current, open circuit voltage, fill factor, stability, improved dye takeup, and ease of fabrication. Said properties being with reference to a similar DSSC prepared under similar conditions but without said ALD layer efficiency.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or are common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.